Transtemporal craniotomy and extradural exposure of the right trigeminal nerve. For orientation, superior is toward the bottom border of the image; inferior is toward the top border, and anterior is toward the left border. The temporalis muscle has been divided near the zygomatic arch anterior to the ear. A large transtemporal craniotomy with elevation of the temporal lobe and division of the tentorium cerebelli has enabled visualization of the middle cranial fossa and the lateral wall of the cavernous sinus. Surgical triangles (anteromedial, anterolateral) of the middle fossa are also demonstrable. The trigeminal (CNV) nerve leaves the lateral pons, travels in the prepontine cistern before passing over the apex of the petrous temporal bone, and entering Meckel's cave, a CSF-filled dural recess that contains the trigeminal (Gasserian) ganglion. This conduit connects the posterior cranial fossa to the middle fossa. The trigeminal ganglion rests upon the trigeminal impression on the petrous apex and medial to the trigeminal prominence, a raised area on this portion of the petrous bone. The petrous segment of the internal carotid artery lies medial to the ganglion within the petrous bone. From the convex margin of the ganglion arise the ophthalmic (CNV1), maxillary (CNV2),  and mandibular (CNV3) divisions. The anteromedial triangle is bounded by the ophthalmic and maxillary nerves and a line between the superior orbital fissure and the foramen rotundum. The anterolateral triangle is bounded by the maxillary and mandibular nerves and a line between the foramen rotundum and ovale. The ophthalmic nerve converges on the superior orbital fissure to enter the orbit. The maxillary nerve enters the pterygopalatine fossa through the foramen rotundum, while the mandibular nerve passes through foramen ovale to enter the infratemporal fossa. (Image courtesy of PA Rubino)